X-ray tube with reverse position focal spot



Filed June 9, 1961 llllllllI/l/I/l/l/l) 3, 1963 R. F. KASTEN, JR., ETAL X-RAY TUBE WITH REVERSE posmon FOCAL SPOT I I I I l I INVENTORS. ROY F. KASTEN, JR. ROBERT M. GAGER BUCKHORN, CHEATHAM 8 BLORE ATTORNEYS Fig.

Ll I ll l United States Patent 3,113,233 X-RAY TUBE WITH REVERSE PGSITHON FQCAL SPUT Roy F. Kasten, Jr., and Robert M. Gagcr, Chicago, Ill.,

assignors to Dunlee Corporation, Eellwood, 11.5., a corporation of lllinois Filed June 9, 1961, Ser. No. 116,160 Claims. (Cl. 313-49) The present invention relates to X-ray apparatus and more particularly to new and improved X-ray generators having a rotary anode.

X-ray generators of the rotary anode type in general use today are provided with anode structures which are of generally convex configuration on the surface facing the cathode. The electrons generated at the cathode are focussed upon such an anode so as to strike a frusto-conical surface near the periphery thereof, and the geometry of the generator is such that the generated X-rays are emitted through an immediately adjacent portion of the envelope of the generator. For certain installations such a geometry is disadvantageous. For example, in fluoroscopy work it is desirable to mount the generator so that the source of X-rays, that is, the focal spot on the anode target upon which the electrons from the cathode are focussed, is a given minimum distance from the subject being X-rayed so as to give improved resolution and minimize the exposure of the patient to X-radiation. Space limitations frequently make it difficult to arrange the generator so that it is spaced at least such minimum distance from the subject being examined.

It is, accordingly, a principal object of the invention to provide a new and improved X-ray apparatus that will alleviate some of the problems mentioned immediately above.

More particularly, it is an object of the invention to provide a rotary anode type X-ray generator wherein the generated X-rays traverse a substantial portion of the generator thereby effectively lengthening the overall length of the path of the generated X rays to a subject without increasing space requirements.

Still another object is to provide a rotary anode type X-ray generator of the type just described with the anode so designed as to remove the fastening means for the anode target member from the path between the focal spot and the subject under examination.

Other objects and advantages of the invention will become apparent in the following detailed description of the invention, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevation partly in section of an X- ray apparatus made in accordance with the invention;

FIG. 2 is an end view of an anode target looking in the direction of the arrows 22 of FIG. 1;

FIG. 3 is an elevation partly in section of a preferred embodiment of the invention; and

FIG. 4 is a view of the target member of the embodiment of FIG. 3 looking in the direction of the arrows 44 of FIG. 3.

Referring first to FIGS. 1 and 2, there is there illustrated an X-ray generator or tube mounted by suitable means (not shown) within a conventional coaxial housing 11 having a window 13 for the emission of X-rays.

The housing 11 is shown positioned beneath a table 12 which may be the supporting table for a fiuoroscopy unit and upon which a patient or object to be fluoroscoped is positioned. The generator 10 comprises an envelope 15 which may be of glass or other suitable material and in one end of which is mounted a cathode assembly 14 which includes a filament 16 adapted to generate and focus a beam of electrons 18 upon a concavo-convex target member Ztl of tungsten or other suitable material forming part of an anode assembly 22. Suitable leads 23 are provided for connecting the filament to a source of electrical energy and it will be understood that the anode and cathode are adapted to be connected to a suitable source of electrical potential which will cause electrons generated at the filament 16 to be propelled to the anode target member 20. The anode assembly 22 is suitably supported within the envelope 12 and includes a rotor 24 from which extends a stem 26 upon the distal end of which the target member 26 is secured with its concave face facing toward the cathode 14. The target member 20 is held in place against a flange 27 by means of a nut 28 which is of lesser height than the amount of indentation of the face of the target member 20.

The mounting of the target member 20 is to be compared with the conventional arrangement of the prior art wherein the anode targets presented a convex face toward the cathode. See, for example, the patent to Atlee 2,786,954, issued March 26, 1957.

The front face of the target member 29 is formed with a frusto-conical surface portion 32 which is coaxial with the axis of rotation of the target member. As shown in FIG. 2 the electron beam 18 is arranged to strike the surface portion 32 in a substantially rectangular focal spot 34 and from which spot X-rays will emanate. The housing 11 and generator 19 are tilted with respect to the table to provide a useful beam uniformly divergent from a line through the focal spot area and perpendicular to the table. As is apparent in FIG. 1, the focal spot 34 is on the far side of the target member 20 with respect to the housing window 13 so that X-rays emitted through the window have to traverse substantially the entire width of the generator. t will be appreciated that X-rays emanate from the focal spot 34 in substantially all directions. However, the target member 26 and the cathode structure will define a useful field which in cross-section subtends an angle b of about 30 lengthwise of the envelope and into which field the nut 28 does not protrude because of the concave configuration of the target member. It will be appreciated that if the generator 10 was provided with a conventional convex target the generator would have to be rotated about its axis, so that the focal spot would be on the upwardly facing surface portion of the target and with the housing 11 in the same position relative to the table 12, closer to the subject being X-rayed so that poorer resolution would result. Thus, the generator 10 enables improved resolution and less overall exposure though the generator is positioned at the same distance as prior art generators from the object being X-rayed.

Preferably, the nut 28, the entire surface of the targe member except the target area 32, are provided with a coating of a material of low atomic number, e.g., graphite or beryllium so as to minimize the emission of radiation from such areas.

Referring now to FIGS. 3 and 4, the preferred embodiment of the invention comprises a generator to including an elongate envelope 42 suitably supported within a coaxial housing 44 mounted beneath a table 4-5 and with the axis of the envelope tilted with respect to the housing axis for reasons to be explained. The generator it? includes a cathode assembly 14 having a filament 16 for generating and focussing a beam of electrons =18 toward the anode target member 4-6 which also presents a concave face toward the cathode but the target area 48 of which is plane and perpendicular to the axis of the anode stem 26'. The central portion 50' of the target member 46 is indented with respect to the surface of the tar-get area 48, the indentation being greater than the height of the nut 28' which secures the target member upon the stem 26' so that the nut 28' does not protrude beyond the plane of the target area 43. Preferably, the surface of the portion 50 and the nut 28 are coated with a low atomic material such as graphite or beryllium.

As shown in FIG. 3, the electrons are focussed to strike the target area in a rectangular focal spot 52 on the side of the anode most remote from the housing window 54 so that as in the previously described embodiment the X-rays emitted from the focal spot '52 traverse substantially the entire width of the envelope 42 and thus the focal spot is spaced a relatively greater distance from the table 45 than would be the case if the conventional convexly faced anode were utilized. The generator 40 and housing 44 preferably are tilted with respect to the table 45 to provide a useful beam uniformly divergent from a line through the focal spot area and perpendicular to the table.

The indentation of the target member 46 is of advantage in that it removes the nut 28' from the useful field so that it will not cast a shadow on the X-ray picture obtained. The advantages of the increased focal spot to subject distance which is obtained, of course, also with the present embodiment, have been mentioned above. As will be further apparent, the present embodiment permits more efiicient employment of the line focus principle to secure the apparent square focal spot as viwed from the table 45.

Having illustrated the described certain preferred embodiments of the invention, it should be apparent to those skilled in the art that the invention permits of modification in arrangement and detail. We claim as our invention all such modifications as come within the true spirit and scope of the appended claims.

I claim:

1. An X-ray tube comprising an elongate envelope, a cathode mounted in one end of said envelope and a rotary anode in the opposite end, said anode comprising a rotor and a stem protruding coaxially from said rotor toward said cathode, a circular, disc like target member having a front and a rear face and having a central aperture receiving the distal end of said stem, said stem having a shoulder thereon spaced from said distal end engaging said target member rear face, said distal stem end being threaded, a fastener element secured on said stern and engaging said target member front face to clamp the target member against said shoulder, said target member having on its front face an annular target area the surface of which is plane and perpendicular to the axis of said stem, means in said cathode for generating and focusing upon said target area a beam of electrons rectangular in cross section and having its longer axis extending radially with respect to said stem axis, the central portion of said target member being indented with respect to said surface, said fastener element having a height less than the amount of said indentation so that no portion of said element projects beyond the plane of said target area, whereupon said fastener element does not project into the useful beam of X-rays emitted from the focal spot of said electron beam as viewed from a position diametrically opposite said focal spot with respect to said stem axis.

2. An X-ray tube comprising an elongate envelope, a cathode mounted in one end of said envelope and a rotary anode in the opposite end, said anode comprising a rotor and a stem protruding coaxial ly from said rotor toward said cathode, a plate like target member of substantially uniform thickness throughout having a central aperture receiving the distal end of said stem, said stem having a shoulder thereon spaced from said distal end engaging said target member, said distal stem end being threaded, a nut threaded on said stem and engaging said target member to clamp the same against said shoulder, said target member having an annular target area facing said cathode the surfce of which area is plane and perpendicular to the axis of said stem, the central portion of said target member being indented with respect to said surface, said nut having a height less than the amount of said indentation so that no portion of said nut projects beyond the plane of said target area.

3. An X-ray generator comprising an envelope, a rotary anode, and a cathode mounted in opposing relation, said anode comprising a solid, platelike, circular target mem ber having an axis of rotation coincident with the longitudinal axis of said envelope, said target member being concave on the surface thereof facing said cathode and being formed with an annular, concave, frusto-conical surface portion coaxial with said axis of rotation and defining a target area, said cathode comprising means for generating and focusing a beam of electrons upon said firusto-conicall surface portion, said beam being of rectangular cross section with the longer axis thereof extending radially with respect to said axis of rotation.

4. An X-ray tube comprising an elongated envelope, a rotary anode comprising. a disc like target member mounted in one end of said envelope, a cathode mounted in the opposite end of said envelope having means displaced from the axis of rotation of said anode for generating and emitting toward said anode a beam of electrons, the paths of said electrons being substantially parallel to said anode axis, said beam being of rectangular cross section with the longer axis thereof substantially radial to said anode axis, said target member being concave on the surface thereof facing said cathode, said surface having a frusto-conical portion coaxial with said anode axis and defining a target area, said electron beam being focused upon said target area, whereby the focal spot of said electron beam upon said target area as viewed from a point lying along a line substantially perpendicular to said electron beam and extending through said anode axis is substantially a square, said anode surface with the exception of said target area being coated with a material of low atomic number.

5. An X-ray tube comprising an elongate envelope, a rotary anode mounted in one end of said envelope for rotation about an axis substantially parallel to and coincident with the axis of said envelope, a cathode mounted in the opposite end of said envelope having means displaced from said anode axis for generating and emitting toward said anode a beam of electrons, the paths of said electrons being substantially parallel to said anode axis, said beam being of rectangular cross section with the longer axis thereof substantially radial to said anode axis, said anode comprising a rotor and a stem protruding coaxially from said rotor toward said cathode, a disc-like target member mounted on the distal end of said stem, said target member being concave on the surface thereof facing said cathode, said surface having a frusto-conical portion coaxial with said anode axis and defining a target area, said electron beam being focused upon said target area, whereby the focal spot of said electron beam upon said target area as viewed from a point lying along a line substantially perpendicular to said electron beam and extending through said anode axis is substantially a square, a fastener element secured on said stern in engagement with the face of said anode target member facing said cathode and securing said target member to said stem, said fastener element having a height less than the amount of indentation of said target face so that no portion of said fastener element projects beyond the plane defined by the forward edge of said target member.

References Cited in the file of this patent UNITED STATES PATENTS 2,345,723 Atlee et a1 Apr. 4, 1944 6 Fenner et a1. Sept. 4, 1956 FOREIGN PATENTS Great Britain Mar. 12, 1941 Great Britain Oct. 13, 1954 Germany Feb. 12, 1931 Germany Nov. 25, 1937 Germany Sept. 6, 1956 

1. AN X-RAY TUBE COMPRISING AN ELONGATE ENVELOPE, A CATHODE MOUNTED IN ONE END OF SAID ENVELOPE AND A ROTARY ANODE IN THE OPPOSITE END, SAID ANODE COMPRISING A ROTOR AND A STEM PROTRUDING COAXIALLY FROM SAID ROTOR TOWARD SAID CATHODE, A CIRCULAR, DISC LIKE TARGET MEMBER HAVING A FRONT AND A REAR FACE AND HAVING A CENTRAL APERTURE RECEIVING THE DISTAL END OF SAID STEM, SAID STEM HAVING A SHOULDER THEREON SPACED FROM SAID DISTAL END ENGAGING SAID TARGET MEMBER REAR FACE, SAID DISTAL STEM END BEING THREADED, A FASTENER ELEMENT SECURED ON SAID STEM AND ENGAGING SAID TARGET MEMBER FRONT FACE TO CLAMP THE TARGET MEMBER AGAINST SAID SHOULDER, SAID TARGET MEMBER HAVING ON ITS FRONT FACE AN ANNULAR TARGET AREA THE SURFACE OF WHICH IS PLANE AND PERPENDICULAR TO THE AXIS OF SAID STEM, MEANS IN SAID CATHODE FOR GENERATING AND FOCUSING UPON SAID TARGET AREA A BEAM OF ELECTRONS RECTANGULAR IN CROSS SECTION AND HAVING ITS LONGER AXIS EXTENDING RADIALLY WITH RESPECT TO SAID STEM AXIS, THE CENTRAL PORTION OF SAID TARGET MEMBER BEING INDENTED WITH RESPECT TO SAID SURFACE, SAID FASTENER ELEMENT HAVING A HEIGHT LESS THAN THE AMOUNT OF SAID INDENTATION SO THAT NO PORTION OF SAID ELEMENT PROJECTS BEYOND THE PLANE OF SAID TARGET AREA, WHEREUPON SAID FASTENER ELEMENT DOES NOT PROJECT INTO THE USEFUL BEAM OF X-RAYS EMITTED FROM THE FOCAL SPOT OF SAID ELECTRON BEAM AS VIEWED FROM A POSITION DIAMETRICALLY OPPOSITE SAID FOCAL SPOT WITH RESPECT TO SAID STEM AXIS. 